A closer look shows Apple’s A4 is “tailored,” not “bespoke”

The closest public analysis done yet of Apple's A4 chip confirms more of what …

Analysis of Apple's A4 didn't stop in the month after the iPad's launch—a number of groups have continued to poke, prod, and photograph Apple's chip, looking for insight into a question that will be familiar to longtime Apple watchers who remember the 68K and PowerPC eras. That question is this: what, exactly, is Apple's processor strategy?

In the current mobile space, just as in the desktop PC space of the pre-Intel era, that larger question of strategy implies a host of smaller questions, like just how much influence do Apple's in-house hardware teams exert over the designs, and where is that influence manifested? What is Apple's long-term plan for playing in the hardware market, and does the company really expect to pit its boutique, Apple-specific designs against the wider commodity market and win?

The EETimes is hosting the latest and most in-depth attempt to understand the nature of Apple's A4—the chip's origins and what it says about Apple's plans. If you're up for it, it's best to look through the whole thing, but I'll give some highlights and takeaways here.

The first takeaway is that, contrary to a popular and recent rumor that has bubbled up in Macdom, the A4 and the Samsung chip that will be used in the upcoming Galaxy S smartphone (the S5PC110) are not the same processor. The two chips are, however, very close, and have the same CPU core. Close visual inspection shows that the two parts sport identical Cortex A8 cores, a fact that should put to rest any notion that PA Semi had anything to do with designing the processor core.

Though it's not 100 percent certain (at least to my knowledge), it's widely and reasonably believed that the 1GHz, 45nm S5PC110 uses the "Hummingbird" A8 variant developed by Intrinsity. If this rumor is in fact true—and it's quite difficult to imagine that it isn't, given that Hummingbird's main claim to fame is that it gets the A8 up to 1GHz on 45nm—then the A4's core is an Intrinsity-designed Hummingbird, as well.

Of course, we already knew this to be the case, but now we really know it. To my mind, the new die shots put the question to rest definitively: Intrinsity designed the Hummingbird core for Apple and Samsung to use in their respective ARM A8 SoCs, and then got itself bought by Apple.

The second takeaway from the EET analysis is the confirmation of another widely held belief, namely that what's "custom" about the A4 is not necessarily any of the individual components, but rather the arrangement. Outside of the Intrinsity-supplied Hummingbird core, the other blocks on the die appear to be from Samsung's standard cell library. What this means is that the A4 and the S5PC110 differ only in the arrangement and mix of these noncore blocks (e.g., graphics and I/O).

The third conclusion, again merely further confirmation of what we already know, is that A4 is an evolutionary design that draws from both the S5PC110 and the iPhone 3GS SoC and makes changes by adding and subtracting blocks. And following on this, the final takeaway is that it's quite hard to see P.A. Semi's fingerprints on the A4. The P.A. Semi team, or whatever's left of it inside Apple, certainly didn't design the CPU core, but they may have had some input in assembling the larger SoC out of parts from Samsung's library.

A final bit that the EET group picked up on was the following detail, which I'll quote in full:

At the 27:30 mark of his January keynote, Steve Jobs introduced the A4, but he actually suggests it is not the first custom Apple design. "We have an incredible group that does custom silicon at Apple." He goes on to say that the A4 is, "our most advanced chip we've ever done." That's a pretty good hint they've been at it for a while.

In other words, the A4 is really sort of a coming out for Apple as an SoC designer, and not so much the start of a new era. With the A4, Apple is making a deliberate move to identify itself as a hardware design shop with plans for the ARM space, and not just another Samsung customer.

There are a few ways that Apple's increased level of involvement and visibility in the SoC design space makes sense: 1) Apple intends to sell so many products with its custom SoCs that it will easily recoup the money; 2) for whatever reason, Jobs has always had a thing for powering Apple products with boutique processors that he can talk up in keynotes; and 3) Apple has so many tens of billions in cash right now that it can drop $50 million here and there on a semi acquisition in order to indulge Jobs' quirks.

Note that one motivation that I don't ascribe to Apple is a genuine expectation that the A4 will provide some kind of real price, performance, or efficiency differentiation in the mobile space. Apple is much better positioned to gain significant, market-moving leadership in these areas via software than it is via hardware.

Sure, customization might buy it a few percentage points vs. the commodity competition in one or all of these areas, but mass-market semiconductors are one place where boutique always loses out to commodity, period. This is even more true in a market like smartphones, which are about industrial design, functionality, UI, software availability and stability, ecosystem size, and a host of other factors that are relatively far removed from the world of "we got an extra 15 minutes of battery life and a 10 percent lead in the Sunspider benchmark."

In a way, it's ironic that Apple tried so long for CPU performance leadership on the desktop by using third parties that could never maintain it (and then caved and just went with commodity x86). Now, it seems that it is actually poised to get a real and possibly durable measure of performance leadership with its custom SoCs, it doesn't matter nearly as much.